Area Forecast Discussion
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000 FXUS61 KPBZ 201710 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 110 PM EDT WED AUG 20 2014 .SYNOPSIS... OCCASIONAL SHOWERS AND THUNDERSTORMS CAN BE EXPECTED THROUGH THE WEEKEND AS A SERIES OF DISTURBANCES MOVE THROUGH THE REGION. && .NEAR TERM /THROUGH TONIGHT/... FLOODING ISSUES CONTINUE ACROSS THE WARNED AREAS DESPITE BATCH OF HEAVY RAIN HAS FINISHED AND MOVED EAST. RECENT SATELLITE IMAGERY TRENDS DISPLAY DRY AIR ALOFT MOVING ACROSS THE OHIO VALLEY BEHIND THE PASSING SHORTWAVE. DESTABILIZATION IS CONTINUING THIS AFTERNOON...ESPECIALLY WHERE CLEARING IS OCCURRING...WITH HIGH SURFACE MOISTURE IN PLACE. SLOW MOVING UPPER LEVEL LOW OVER THE GREAT LAKES GENERATING A SHORTWAVE MAY PROGRESS EAST TOWARDS THE FORECAST AREA THIS AFTERNOON TO HELP INITIATE CONVECTION. THUS...HIGH CHANCE POPS WERE MAINTAINED THROUGH THE EVENING TO WHERE THE SURFACE BOUNDARY IS DRAPED ACROSS. CONVECTION IS THEN EXPECTED TO DECREASE LATER THIS EVENING WITH THE LOSS OF HEATING AND DISPLACEMENT OF THE SHORTWAVE. TEMPERATURES ARE EXPECTED TO BE SLIGHTLY ABOVE NORMAL FOR TODAY AND TONIGHT. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... A RELATIVELY STATIONARY BOUNDARY STRETCHING SOUTH FROM A WEAK SFC LOW WILL REMAIN IN THE AREA THURS THROUGH FRI WITH SEVERAL DISTURBANCES PROGGED TO TRAVERSE ALONG IT. SHOWERS AND THUNDERSTORMS SHOULD QUICKLY DEVELOP THURS AS THE BOUNDARY LAYER DESTABILIZES AROUND MIDDAY. WHILE THE BEST INSTABILITY AND SHEAR APPEAR TO STAY SOUTH OF THE BOUNDARY THURS...OVER SRN OH...WHERE SPC HAS INCLUDED A SEE TEXT PORTION OF THE DAY TWO OUTLOOK. MEANWHILE...THE 00Z NAM SHOWS AROUND 1500J/KG SFC CAPE AND 30-40KTS 0-6KM BULK SHEAR IN OUR AREA. THE CORE OF THE H5 JET REMAINS OVER SWRN OH. COULD EXPECT A FEW STRONG TO SEVERE THUNDERSTORMS THURS AFTERNOON/EVENING. EXPECTING TO SEE A DIURNAL LULL LATER THURS INTO EARLY FRI...BUT WITH ENOUGH MOISTURE PRESENT ALONG THE BOUNDARY...SHOWER CHANCES WILL EXIST...MAINLY INTO ERN OH. FRIDAY AS THE UPPER RIDGE TRIES TO BUILD OVER THE MS VALLEY...A SFC LOW LIFTS THE BOUNDARY NORTH AS A WARM FRONT SERVING AS A FOCUS FOR ADDITIONAL SHOWERS AND THUNDERSTORMS. A WAVE AT H7 WILL MOVE ALONG THE BOUNDARY AGAIN FRI...BUT TIMING DIFFERENCES EXIST AMONG THE MODEL GUIDANCE. AT THIS POINT WILL CONTINUE TO CARRY HIGH CHC POPS FOCUSED ON THE EARLY EVENING TIMING OF THE 00Z NAM/ECMWF. PWAT VALUES MAX OUT AROUND 2" FRIDAY THROUGH ERN OH AND NRN WV ALONG THE CORRIDOR WHERE SHOWERS AND THUNDERSTORMS ARE EXPECTED. STORM MOTIONS FROM THE 00Z NAM BUFR SOUNDINGS ARE IN THE 20-30KT RANGE...BUT SHOWERS SHOULD BE HIGHLY EFFICIENT AND ANY TRAINING COULD LEAD TO WATER PROBLEMS THROUGH FRI NIGHT. TAX && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... WITH ACTIVE WEATHER IN THE NEAR TERM...GENERALLY STAYED CLOSE TO THE PREVIOUS FORECAST BLENDING WITH WPC THINKING FOR THE EXTENDED PERIOD. MODELS CONTINUE TO SHOW A RIDGE BUILDING IN THE SRN PLAINS THROUGH THE WEEKEND...SLOWLY SHIFTING THE AXIS INTO OUR REGION BY EARLY NEXT WEEK. THE WEEKEND WILL REMAIN WARM AND MUGGY WITH DAILY RAIN CHANCES AS WE SIT ON THE ERN PERIPHERY OF THE RIDGE. A GRADUAL EASTWARD SHIFT IN THE UPPER TROF AXIS WOULD MEAN A CONTINUATION OF AT LEAST NEAR NORMAL TEMPS THROUGH MIDDLE OF NEXT WEEK WITH A DRYING TREND. TAX && .AVIATION /17Z WEDNESDAY THROUGH SUNDAY/... SHOWERS AND EMBEDDED THUNDERSTORMS HAVE CONGEALED INTO A RAGGED MCS THIS MORNING. MAIN LINE OF THUNDER IS HEADING THROUGH EASTERN OHIO CURRENTLY...AND HAVE TRIED TO TIME TEMPO IFR VSBYS THROUGH HLG/PIT/AGC/BVI OVER THE NEXT COUPLE OF HOURS. THINK THE LINE WEAKENS BEFORE IT IMPACTS TERMINALS TO THE EAST. A RELATIVE LULL WILL BE SEEN LATER THIS MORNING...WITH MOST LOCATIONS POSSIBLY ACHIEVING VFR. INSTABILITY SHRA/TSRA ARE THEN EXPECTED THIS AFTERNOON ASSUMING WE GET A BIT OF SUN. MAINTAINING VCTS FOR NOW AS AM STILL UNCERTAIN ON TIMING AND AREAS OF HIGHEST PROBABILITY. ACTIVITY SHOULD START TO WEAKEN AFTER SUNSET. THINK CLOUDS BREAKUP SOMEWHAT AS WE WILL LIKELY BE IN BETWEEN DISTURBANCES. HAVE MVFR FOG MENTIONED AT MOST SITES OVERNIGHT...AND THIS MAY BE OPTIMISTIC AT A FEW. OUTLOOK.../WEDNESDAY NIGHT THROUGH SUNDAY/... SEVERAL CROSSING DISTURBANCES WILL CAUSE PERIODIC RESTRICTIONS INTO THE WEEKEND. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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